1. Field of the Invention
This invention pertains to a multiple speed ratio automatic transmission for use with an electrically driven automotive vehicle.
2. Description of the Prior Art
Conventional automatic transmissions used in vehicles powered by internal combustion engines are not readily adapted for use in an electrically driven vehicle. The parasitic losses associated with operation of the hydraulic pump, control system and torque converter could reduce the operating range of an electrical vehicle by approximately 15 percent. Furthermore, certain major automatic transmission components such as the hydrokinetic torque converter and reverse gearing are unnecessary in an electric vehicle that uses an a.c. induction motor whose rotation can be reversed. Also the final drive or axial ratio used with conventional automatic transmissions would limit the operating speed of the electrical motor and this would result in substantial cost, weight and size penalties.
The most favorable balance among costs, weight, efficiency and package size for an electric vehicle powertrain is realized with electric motors that operate in the range between 8000 and 10,000 rpm with an automatic transmission compatible with these speeds. An automatic transmission develops the maximum vehicle driving range through efficient control of the motor operation and because regenerative braking, which recovers braking energy to recharge the propulsion battery, can be readily incorporated.
A variety of motor-transmission configurations are possible in the front wheel drive vehicles. Two or three rotational axes interconnected by gear or chain transfer drives are generally employed to provide step transmission ratios and the final drive ratio. The differential double gear system is usually located on the drivewheel axis. A front wheel drive system wherein the motor and transmission are mounted transversely with respect to the fore and aft axis of the vehicle, must be a highly compact unit and preferably one in which the high speed a.c. motor, automatic transmission and final drive have a common axis with the wheel axis.